Answer:
Well, I'd say because of bipedalism (standing and walking up-right).
Step-by-step explanation:
Favoring vision among our other four senses is seen as a consequence of how human evolution has developed so far. Thanks to bipedalism we could free our hands from the ground, then, we started using tools better; we gained a way of saving energy when commuting for long distances; and we allowed our selves to have a wider field of vision, which helped us in many ways, but especially in preventing attacks from predators.
This last evolutionary feature is what originated our nowadays-very-accute vision.